BMW Questions? Ask a BMW Repair Expert for Answers.
I believe that our P0491 code could be caused by a broken secondary air supply tube under the intake manifold. Number 1 in the picture below.
For your smoking issue you might have a vacuum leak sucking oil in, but it is also possible that you have a valve seal issue. Your best bet is to take the car to a shop that can smoke check the intake system and see where the leak is.